Hello Rolf,

It can take quite a bit of time to get the air out of the diesel set up.
After every short drive for a few weeks duration you can open the
bleeder valve to let out the air that has built up. Do not wait until
the pressure builds up, it can be quite explosive. You may just have air
stubbornly remaining in the system and/or air getting in somewhere. Air
can get in and you may not see any obvious external evidence. Hairline
cracks on the expansion tank air can be sneaking through where the
temperature sender is fitted to the expansion tank.
I do not know if a malfunctioning water pump could contribute to this
air problem, at least you can easily observe if the cooling liquid is
being pumped around.
 I can smell a leak before seeing it.

> can't get engine to hold at @ 2000 RPM - injection pump seems to want to race
> above a certain setting,
First thing to check there, is the nuts/bolts/bushings that secure the
pump to the mounting plates. Second is that there are two clamps on the
fuel lines. Any extra vibration with the pump/fuel lines affect the rpm
as if the  acceleration cable is stuck. With the engine's rpm stuck
high, hold the pump/fuel lines with very firm pressure and observe if
the rpm's drop.

regards, Martin Kennelly